This invention relates to the field of lift trucks, and more particularly to means for securing a lift mast assembly to the front of a lift truck frame. Prior art arrangements have provided pairs of spaced parallel bracket members secured to the rear of the mast uprights and having axially aligned bores therein which rotatably receive support shafts therein which have a rectangular cross sectional central portion disposed between the brackets.
The rectangular central portions of the support shafts are cradled in upwardly opening slots formed by J-hook members provided on the front of the lift truck frame. In the past, the support shafts have been retained within the slots by retainer plates that are bolted to the J-hook members immediately above the central portions of the pivot pins disposed in the slots. The retainer plates have lower edges that bear against the support shafts and retain them securely in the J-hook slots.
The mast asembly may be removed from the lift truck by removing the bolts securing the retainer plates to the J-hooks, removing the retainer plates, and lifting the mast assembly until the support shafts clear the front of the slots.
The foregoing arrangement has many attractive features and advantages. However, one problem that has been encountered is that it requires close tolerances to insure that the bottom edges of the retainer plates will bear firmly against the central portions of the support shafts when the retainer plates are secured for the J-hooks by the securing bolts which pass through suitable bores in the retainer plates and threadably engage the J-hook members in threaded bores provided therein.
Another problem encountered has been shearing of the the retaining bolts when sudden up-loads on the mast assembly are encountered, such as when the left truck runs the mast assembly, or the forks mounted thereon, into the ground, or another object.